Plastic plating process and solution therefor

ABSTRACT

A process for the plating of a non-metallic material, such as polyethylene or polypropylene strip, which includes the step of immersing said material in an alcohol solution containing boron, phosphorous and a metal selected from the group consisting of gold, palladium, rhodium and platinum. The metal film forms adherently on the strip. The solution is prepared by mixing phosphorous pentoxide in an alcohol solvent. The dissolution of the phosphorous pentoxide is exothermic and the temperature of the solution will rise during the reaction. Then, boric anhydride and a salt of gold, palladium, rhodium or platinum is added. The solution appears to strip any contamination while depositing a layer of the gold, platinum, rhodium or palladium onto the surface of the non-metallic part. The process is particularly advantageous for preparing metallized strips for use during semiconductor device assembly.

United States Patent 11 1 Flowers [451 Aug. 5, 1975 1 PLASTIC PLATINGPROCESS AND SOLUTION THEREFOR [75] Inventor: Dervin L. Flowers,Scottsdale, Ariz.

[73] Assignee: Motorola, Inc., Chicago, 111.

[22] Filed: Dec. 26, 1973 21 Appl. No.: 428,473

Primary Examiner-Cameron K. Weiffenbach ASSiSIunt E.\'atninerCharles R.Wolfe, Jr.

Attorney, Agent, or Firm-Vincent J. Rauner; Henry T. Olsen 5 7 ABSTRACTA process for the plating of a non-metallic material, such aspolyethylene or polypropylene strip, which includes the step ofimmersing said material in an alcohol solution containing boron,phosphorous and a metal selected from the group consisting of gold,palladium, rhodium and platinum. The metal film forms adherently on thestrip. The solution is prepared by mixing phosphorous pentoxide in analcohol solvent. The dissolution of the phosphorous pentoxide isexothermic and the temperature of the solution will rise during thereaction. Then, boric anhydride and a salt of gold, palladium, rhodiumor platinum is added. The solution appears to strip any contaminationwhile depositing a layer of the gold, platinum, rhodium or palladiumonto the surface of the non-metallic part. The process is particularlyadvantageous for preparing metallized strips for use duringsemiconductor device assembly.

3 Claims, N0 Drawings PLASTIC PLATING PROCESS AND SOLUTION THEREFORRELATED APPLICATION This invention is related to application Ser. No.414,587, filed Nov. 9, 1973.

BACKGROUND OF THE INVENTION This invention relates to the plating ofnon-metallic parts and, more particularly, to the plating of plasticfilms such as polyethylene or polypropylene.

To produce a metallized non-metallic member such as a ceramic, it haspreviously been a practice to at least initiate plating by a vacuumvaporization metallization process. This relatively high temperatureprocess cannot be utilized for plastic materials having lower meltingpoints. In these latter cases, it was necessary to laminate a metal filmthereto or coat a strip as by painting. These processes do not producethe adherency of a plating.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved process for the cleaning and plating of nonmetallic parts orstrips.

A further object of the invention is to provide a process for theplating of low temperature plastics, such as polyethylene orpolypropylene.

In accordance with these objects, there is provided a process for thestabilization and cleaning of a nonmetallic part which comprises thestep of immersing said lead frame in an alcohol solution containingboron, phosphorous and a metal elected from the group consisting ofgold, palladium, rhodium and platinum.

Further objects and advantages of the invention will be understood fromthe following complete description thereof.

COMPLETE DESCRIPTION In accordance with the particular embodiment of theinvention, the process is one for removing organic contamination from anon-metallic part prior to plating. During this process, the everpresent skin of oxide is also removed. Both the organic contaminationand the oxide contamination act to inhibit the adherency and quality ofthe plating. During the present process, the part is simultaneouslyplated with an inert noble metal, which prevents regrowth of a new layerof oxide on the part, as would happen if it is subsequently exposed toair prior to plating or metallization.

The process comprises coating a non-metallic material with a complexsolution consisting essentially of l to 30 grams per liter phosphorouspentoxide, l to 60 grams per liter boric anhydride, 0.01 to 10.0 gramsper liter of a material selected from the group consisting of gold,platinum, palladium and rhodium salts and oxide, and the balance asolvent selected from the group consisting of methyl, ethyl, propyl,isopropyl, butyl, and isobutyl alcohol, ethylene glycol and tetrahydrofurfuryl alcohol.

The process functions by deposition from a selected organic solvent of athin adherent layer of an inert noble metal, such as gold, palladium,platinum or rhodium, on the aluminum. The noble metal layer may be mademono-atomic in thickness, or, depending on time, films of severalmicrons may be plated, and is stable to ambient conditions oftemperature and humidity.

The solution used in the process is a solution of phosphorous pentoxide,boric anhydride and a noble metal salt, such as potassium, gold cyanide,potassium gold chloride, palladium chloride or similar salts of rhodiumand platinum. A concentration of dissolved solids of from 0.5 to 4percent with an atomic ratio of phosphorous-boron-noble metal of 1:3:O.lhas been used. The phosphorous-boron solution serves as the carrier tosolubilize the noble metal salt.

A typical solution is prepared by dissolving l to 30 grams per literphosphorous pentoxide in various alcohols, such as isopropyl aclohol.This reaction is exothermic and results in a rise in temperature of thesolution. To this solution is added 1 to 60 grams per liter boricanhydride to form a boron/phosphorous ratio in the solution of at least3:1. This ratio is necessary to prevent hygroscopic side effects afterthe solution has been dried following treatment in accordance with theprocess. The foregoing solution forms a stock base solution to which0.01 to 10 grams per liter noble metal salt will be added prior to use.The noble metal salt should not be added too long ahead of use, sinceplating of the noble metal on the container will occur spontaneouslyover a period of a few days. When it is desired to treat the parts inaccordance with the subject process, a sufficient amount of the noblemetal salt is added to the stock base solution to form a ratio ofboron/phosphorous to noble metal of 1:3:O.1. Solution can be generallyeffected by shaking or stirring in a matter of minutes.

To treat the parts in accordance with the process, a preliminarydegreasing in isopropyl alcohol may be utilized, although this is notnecessary. The parts are added to the above disclosed solution at roomtemperature, until an absorption or immersion plating equilibrium isapproached. The solution is then decanted from the parts and the partsare rinsed with an alcohol, such as methanol, and air dried. Preferably,the parts are then baked for 30 minutes in air at 200C. Following thistreatment, the parts are ready for further assembly.

EXAMPLE I A preliminary solution was prepared by dissolving 16 grams ofphosphorous pentoxide in 500 milliliters of isopropyl alcohol. To thissolution is added 28 grams of boric anhydride, which dissolves in amatter of minutes. The solution is then diluted with another 500milliliters of isopropyl alcohol, thus forming a stock solution.

To the foregoing diluted stock solution was then added 2.0 grams ofpalladium chloride. Solution of the palladium chloride was affectedover-night.

A l X 2 X .007 inch test strip of polyethylene when immersed in 250 mlof the above solution in a pyrex beaker at 22C for 24 hours plated a 5 7microinch film of mirror bright palladium. When scratched and probedwith a sharp point, no evidence of delamination was seen at 55X using amicroscope.

EXAMPLE II To 1000 ml of a stock solution prepared as in Example l wereadded 4 grams of palladium nitrate. Solution was affected overnight A lX 2 X .005 inch test strip of polypropylene, when immersed in 250 ml ofthis solution at room temperature, plated a 5-7 microinch film of brightpalladium in 10 hours at 22C that was tightly adhering.

EXAMPLE Ill Five hundred ml of the stock solution in Example I werediluted to l liter with 500 ml of isopropyl alcohol. Four grams ofpalladium chloride were dissolved overnight in this solution. A l X 2 X.007 inch test strip of polyethylene when immersed in this solution 90minutes at 65C plated a mirror bright, tightly adhering film ofpalladium 5-7 microinches thick.

The foregoing process may be utilized in many ways including, but notlimited to, the following:

A. Use in place of evaporation to achieve an electronically cleanconductive (immersion plated) surface prior perhaps to thickerelectro-plating, e.g., the 8 K stack" where 800 A of chromium wereevaporated prior to plating a copper layer. This would not requireexpensive equipment nor clean up time after evaporation on theequipment. No salvage cost and care would be necessary as there is inthe bell jars of evaporators.

B. Deposit on alkali-free plate on plastic parts for later electronicuse where size, shape, angles, blind holes, etc., preclude thepossibility of evaporating such a coating.

C. Place palladium on plastic by this process to provide a clean,alkali-free, conductive surface which also acts as a barrier fordiffusion of alkali ions from the plastic which usually contains suchions present as ad- 4 ditives (antioxidants, fillers, plasticizers, moldrelease agents, etc.).

While the invention has been disclosed by way of certain preferredembodiments andexamples thereof, it will be appreciated that suitablemodifications may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. A process of plating non-metallic material which consists of the stepof coating the material with a complex solution consisting essentiallyof l to 30 grams per liter phosphorous pentoxide, 1 to 60 grams perliter boric anhydride, 0.01 to 10.0 grams per liter of a materialselected from the group consisting of gold, platinum, palladium andrhodium salts and oxide, and the balance a solvent selected from thegroup consisting of methyl, ethyl, propyl, isopropyl, butyl, andisobutyl alcohol, ethylene glycol, and tetrahydro furfuryl alcohol.

2. In a process as recited in claim 1 wherein said coating step includesimmersing a semiconductor device in said complex solution for l 24 hoursat room temperature.

3. In a process as recited in claim 1 wherein said coating step includescovering a surface of a semiconductor device with said complex solutionfor l 24 hours at room temperature.

1. A PROCESS OF PLATING NON-METALLIC MATERIAL WHICH CONSISTIS OF THESTEP OF COATING THE MATERIAL WITH A COMPLEX SOLUTION CONSISTINGESSENTIALLY OF 1 TO 30 GRAMS PER LITER PHOSPHOROUS PENTOXIDE, 1 TO 60GRAMS PER LITER BORIC ANHYDRIDE, 0.01 TO 10.0 GRAMS PER LITER OF AMATERIAL SELECTED FROM THE GROUP CONSISTING OF GOLD, PLATINUM, PALLADIUMAND RHODIUM SALTS AND OXIDE, AND THE BALANCE A SOLVENT SELECTED FROM THEGROUP CONSISTING OF METHYL, ETHYL, PROPYL, ISOPROPYL, BUTYL, ANDISOBUTYL ALCOHOL, ETHYLENE GLYCOL, AND TETRAHYDRO FURFURYL ALCOHOL. 2.In a process as recited in claim 1 wherein said coating step includesimmersing a semiconductor device in said complex solution for 1 - 24hours at room temperature.
 3. In a process as recited in claim 1 whereinsaid coating step includes covering a surface of a semiconductor devicewith said complex solution for 1 - 24 hours at room temperature.